If the smoke was coming from the trigger then I doubt it was the battery as they're in the stock. I'd say it was a problem with either the wiring or the motor.
Imo you did the right thing sending it back. Too many people in this hobby are happy to buy something, find out it doesn't work and then spend more on fixing it. As far as I'm concerned, if I'm spending several hundred quid on something it had better work out of the box or it's going back